1. Field of the Invention
This invention relates to a hydraulic torque converter for vehicles in which the pump wheel and the turbine wheel are connected through a one-way clutch and an on-off clutch, arranged in series with each other.
2. Description of the Prior Art
A direct coupling device of a fluid torque converter for vehicles such as automobiles has been used to increase the torque transmission efficiency by directly connecting the pump wheel and the turbine wheel to minimize the slippage between these elements with no fluid working as a transmission medium. This kind of conventional direct coupling device has a friction clutch interposed between the pump and turbine wheels, which is engaged or disengaged by hydraulic pressure or centrifugal force. When engaged, the friction clutch connects the pump and turbine wheels thereby shifting the power transmission mode from fluid transmission to mechanical transmission. The conventional direct coupling device, however, has a drawback. That is, since during the mechanical transmission no slippage of the friction clutch is permitted, when the fluid torque converter is directly coupled the variation in engine torque will be conveyed directly to the power transmission system. Thus, when the vehicle is abruptly decelerated, a resulting shock is conveyed to the power transmission system giving an uncomfortable feeling to the driver. In this way, although the conventional direct coupling device improves the transmission efficiency, it has the drawback of reducing comfort during driving.